One of the finest books of the series, of a rather dumb brother and clever sister(whose names are Sam and Sally), who is trying to prove to him that the world is round. But the evil master-mind (the school head teacher), sends them on to a one way trip to Pluto. The kids meet some aliens who are scared of the sun dragon's witch are realy just comets. The two go to check it out and they find the aliens hiding in caves. (To pass the time they have ballon races!) When the two say its okay to come out they ask the aliens to see if they've got a ballon to get them back to earth. They attached it to the rocket and blast off to Earth. At the end they land on the beach right where they started. As the story unfolded, more and more laughs appered, they just kept coming atchya!The best book I have read in a long time!